Rethinking Your Garbage

garbageDo you ever wonder what happens to your garbage after you throw it out? While we hope that the recyclable materials we painstakingly sorted out end up being recycled, the garbage usually ends up sitting in the landfill. Although the landfill may be a solution for our “throwaway” society, it isn’t quite a permanent one. Think about how the increasing population on the planet will directly increase the amount of garbage produced, and how land is a precious commodity. As the time increases, the amount of land available will decrease, and 2/3 of the Earth is covered by water anyway. With global warming, more land may become submersed. The ocean isn’t immune to garbage either, as much of it, especially plastic waste, ends up polluting the precious sea life and the water.

According to the Conference Board of Canada, Canada produced 777 kg per capita of municipal waste in 2008. In a study ranking the municipal waste generation of 17 countries, Canada ranked last, meaning that Canada produced the most garbage per person. What’s worse is that Canada’s municipal waste production has been increasing since 1990.  The Conference Board of Canada further states that Canada should learn from other countries such as Japan, the U.K., Sweden, Finland, and Denmark in order to improve their municipal waste management.

Sweden has found a solution in which less than 1 percent of household garbage (municipal solid waste) ends up in landfills, and 99% of the waste is recycled. This is a drastic improvement, since only 38 percent of Swedish household waste was recycled in 1975. How does Sweden do this? First, the Swedes take their recycling very seriously, and recycling stations are situated, “as a rule”, according to Swedish website, no more than 300 metres from any residential area. The garbage that can’t be recycled is incinerated for energy at their 32 specialized waste to energy incineration plants. In 2012, for instance, 2,270,000 tonnes of garbage was incinerated for energy. Sweden also imports 700,000 tonnes of waste from other countries, at a profit, and turns this foreign garbage into energy too.
“Waste to energy”  is the generation of energy, such as electricity and heat, from household garbage (municipal solid waste). Modern waste to energy incineration plants in OECD countries, including those in Sweden, must meet rigid emission guidelines pertaining to levels of toxic emissions such as those of nitrogen oxides, sulphur dioxide, heavy metals, and dioxins. The waste to energy plants utilize furnaces which are fed garbage. The garbage is burnt, producing heat which boils water and generates steam. The steam powers generator turbines that can then produce  electricity and heating. The electricity is distributed across the country. And just like that, in Sweden, 810,000 households are furnished with heating and 250,000 with electricity.

 While Swedish citizens overall don’t seem to be complaining about waste incineration, some people point out that the toxins leaked into the air can be unhealthy for the environment.  Even though emission levels of toxins are controlled for, modern incinerators can still emit small amounts of heavy metals, dioxins, particulates, and acid gas in the fly ash.  Lime scrubbers and electrostatic precipitators are put on smokestacks to filter the smoke and prevent acid rain, while fabric filters, reactors, and catalysts also significantly work on limiting the amounts of released pollutants. Aqueous ammonia can be used to control for the amount of nitrogen oxides, and carbon can help control for the amounts of mercury. Phosphoric acid can be administered to counterbalance the ash.

When it comes to greenhouse gases, methane gas is 21 times more harmful to the environment than carbon dioxide. Landfills in Canada generate a staggering 20% of  the nation’s total methane production. According to Environment Canada, about 27 megatonnes of carbon dioxide equivalent are produced each year from Canada’s landfills, out of which 20 megatonnes of carbon dioxide equivalent are released into the environment annually. About 7 megatonnes of carbon dioxide equivalent are captured from landfills through a gas collection system, and combusted- this has the equivalent effect of taking 5.5 million cars off the road. Much of the carbon dioxide is not captured from landfills. There is also concern that landfill sites are filling up fast, and new sites are increasingly more difficult to find.

Canada needs to step up its waste to energy game. At present, the nation has only 7 waste to energy plants. They are located in Burnaby, BC; Quebec City, QC; Levis, QC; Iles de la Madelaine, QC; Brampton, Ont; Charlottetown, PEI; and Wainright, Alta. The waste to energy plant in Burnaby, BC, for instance, has been successfully operating since 1988. It produces a sufficient amount of electricity to power 16,000 households, earning Metro Vancouver about $6 million from the sale of electricity. About 8000 tonnes of metals are recovered each year, which earns the city $500,000 annually from the sale of recycled metal. More waste to energy plants should be built in Canada in order to divert the nation’s abhorrent trend of landfilling.

New waste to energy technologies are emerging which are even more exciting alternatives to landfills because these don’t require direct combustion, thus preventing fly ash and reducing the amount of bottom ash.  Conversion technologies involve the heating of municipal solid waste at superheated temperatures in an oxygen-controlled environment to deter combustion. Solid waste is converted to usable products such as synthesis gas, which is mainly made of hydrogen and carbon monoxide. This “syngas” can be burned in a boiler to generate electricity, or be processed into a fuel.  In a few years from now, more affordable technology could allow this syngas to be cleaned and purified of contaminants, allowing conversion technologies to become an efficient and cleaner alternative to combustion incineration. Newer technologies do not produce as much bottom ash, a toxic byproduct, as incinerated waste does. 40% of bottom ash produced by incinerating garbage is thrown into the landfill, and 60% of it is further processed to salvage metals. Conversion technologies can collect metals right away, and leave less byproduct to dump into the landfill.

When I think of landfills, I am often reminded of the scene in Idiocracy where the garbage in their landfill is piled up so ridiculously high that it collapses very dramatically. The image serves not only as a direct parable, but as a metaphor too. As the human population increases, so will the amount of garbage produced. Canada is generally known as a progressive country with a high standard of living. As a proud Canadian, I would love to see Canada find a good solution for the management of the population’s garbage.

Sierra Delarosa

 

 

 

 

A Cure for Multiple Sclerosis?

needleA research study published June 2016 in the prestigious journal, The Lancet, details a very risky but effective cure for patients with aggressive multiple sclerosis (1). In multiple sclerosis (MS), the immune system attacks its own insulating material called myelin which usually covers nerve cells in the brain and spinal cord. There is currently no cure, but symptoms may be managed through the use of medications that manage inflammation and inhibit the immune system to dampen further demyelinating damage. Symptoms vary among individuals but can include numbness, weakness in the limbs, loss of balance, fatigue, and blurred vision. More severe cases can involve paralysis. The medical procedure described in The Lancet relies on the harvesting of a patient’s own hematopoietic stem cells to be used as grafts after almost completely destroying the patient’s existing immune system. This autologous hematopoietic stem-cell harvest, which selects for CD34+ progenitor cells, is taken from the patient after stimulation (mobilization) to increase the numbers of circulating myeloid stem cells (2). This is done with the chemotherapy drug, cyclophosphamide, and filgrastim, a granulocyte colony-stimulating factor analog which promotes the rapid increase and differentiation of a type of white blood cell called granulocytes. A cure to MS is possible through the ablation of the current faulty immune system of MS, and the subsequent replacement with hematopoietic stem cells that can then become healthy immune blood cells.

The study began in 2000, and the paper describes Phase 2 of the study at three hospitals in Canada. Twenty-four patients participated, and one has died during the study due to liver complications. The treatment is initially quite toxic, and strong chemotherapy drugs are given to destroy the immune cells. After immune cells are rendered null through the use of busulfan, cyclophosphamide, and rabbit anti-thymocyte globulin, the patient is left vulnerable to infection. The chemotherapy is toxic to sperm or eggs, and women enter early menopause. Hair and fingernails fall off. Yet, MS patients desperately searching for a cure have chosen this option and experienced not only a cessation of symptoms, but also some recovery from previous MS-induced damage. Patients were followed up for up to thirteen years after autologous hematopoietic stem-cell transplantation, and even though they were not on any medications, they were found to be free of relapses and without any new brain lesions in MRI scans.

Interestingly, this process of “resetting” the immune system was found to be effective for MS quite accidentally. Initially, people with both leukaemia and MS were being treated for leukaemia, a cancer of the white blood immune cells. This cancer starts in the bone marrow, so autologous blood stem cells from the bone marrow are first collected and rid of any cancerous cells. The cells are then reintroduced into the body as a graft to elicit new, healthy immune cells after the existing, cancer-ridden immune system is destroyed by toxic chemotherapy. The results were found to be effective not only for leukaemia, but for MS as well. It is hoped that a similar approach can be used to cure other autoimmune diseases such as Crohn’s disease, scleroderma, and lupus. The risk associated with deleting a person’s entire immune system is great, but by adjusting the balance between toxicity and maximal therapeutic results, a safer medical intervention can be found. Larger trials can be conducted to determine the best dosage and effectiveness so that hopes can be high for people suffering from MS and other debilitating autoimmune diseases.

 

Sierra Delarosa

 

References

  1. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)30169-6/abstract
  2. http://www.ncbi.nlm.nih.gov/pubmed/12592344

Hepatitis A From Frozen Berries

berriesOn April 15, 2016, the Canadian Food Inspection Agency (CFIA) announced a food recall warning regarding the possible contamination with Hepatitis A, a viral liver disease, of the frozen fruit product, “Nature’s Touch Organic Berry Cherry Blend”. Canadians have been advised that the food recall is in effect in the provinces of Ontario, Quebec, New Brunswick, Nova Scotia, and Newfoundland and Labrador, where the product has been sold. As of April 22, 2016, there are eleven related Hepatitis A cases in three provinces (1): Ontario (8 cases), Quebec (2 cases), and Newfoundland and Labrador (1 case).

While it is frightening to know that Hepatitis A can be contracted by eating frozen berries, a product that is supposed to be healthy, coming into contact with hepatitis A can be quite easy. Hepatitis A is usually linked with the lack of potable water and inadequate sanitation,  and the virus is spread mainly by the faecal-oral route. It can be acquired from any food and drinks prepared by a person who is infected, as an  infected person can carry, due to improper hygiene, traces of their faeces when preparing refreshments. Shellfish derived from waters containing sewage can also carry hepatitis A. The frozen berries sold at Costco in Canada were at some point contaminated with hepatitis A from at least one infected worker (during harvest, manufacturing or processing) who was handling the berries, and who did not take preventative hygienic measures such as frequent hand-washing with soap and water, and the use of gloves. After infection with hepatitis A, symptoms usually reveal themselves two to seven weeks after viral infection. Fever, loss of appetite, abdominal pain, jaundice, dark urine, vomiting, and fatigue are all symptoms. Although cases usually last one to two weeks, a few severe cases can last several months before recovery, and some people can die from liver failure. People with pre-existing liver conditions are at a greater risk of severe illness. Older people tend to get sicker than younger people after infection.The disease is not chronic (there is usually no permanent liver damage), and lifetime immunity is acquired either from recovery after infection, or through immunization with the hepatitis A vaccine.

The hepatitis A virus, a picornavirus, is of an icosahedral shape and does not contain an envelope. It possesses a single-stranded RNA packaged in a protein capsid. There are three different numbered human genotypes of the virus, but type IA is the most commonly occurring. Genetic sequencing of the virus can reveal which molecular subtype of the virus is associated with a particular outbreak (2), thus narrowing down unassociated cases of infection. To determine whether infection has occurred, a blood test to look for IgM anti-hepatitis A antibodies, a particular immune response, can detect the virus as early as two weeks after the initial infection.

Known as a “traveller’s disease”, hepatitis A is usually associated with countries that are less developed, but it does and can occur in Canada. In industrialized countries, outbreaks of hepatitis A are often linked to contaminated produce (3). During March 2012, there was a small outbreak of hepatitis A in British Columbia, Canada that was traced to pomegranate seeds in a frozen fruit product (4). April 2013 saw more than 70 cases of hepatitis A infection in four Nordic countries (5,6). In the United States, there were 165 confirmed cases of hepatitis A infection found across 10 states, in 2013 (7). This outbreak was traced to pomegranate arils found in a frozen berry product sold at Costco, and 44% of the infected patients were hospitalized. Frozen fruit can last for up to a year in the store, and hepatitis A can incubate for up to 50 days, so a hepatitis A outbreak is often detected only after many people have been infected (8). Case-control studies, where patients with (case) and without (control) a disease, such as hepatitis A, are compared retrospectively for frequency of exposure to a risk factor (such as the contaminated frozen fruit), and through this study method the source of the outbreak can be unraveled.

Costco is publicly offering free vaccination clinics to affected individuals of this recent 2016 outbreak, as vaccination can prevent the disease symptoms from occurring if given within two weeks of exposure (9). There are two options for post-exposure prophylaxis of hepatitis A. The first is the vaccine injection, which is an inactivated version of the virus. The second is immunoglobulin (IG), which is injected and consists of antibodies which fight the virus to prevent infection. It is a blood product produced from paid donors. An exposed individual who may be allergic to the vaccine may opt for the IG. A study comparing the two options found that immunoglobulin was slightly more effective than the vaccine (10). However, the vaccine offers a lifetime immunity, whereas the response of immunoglobulin against hepatitis A is only for three months after the IG administration-subsequent exposure to hepatitis A can still result in an infection. Individuals can get a pre-exposure prophylaxis vaccination, which renders permanent immunity before any exposure, and travellers to countries where hepatitis A is endemic are required to receive the vaccination before leaving to their destination.

The recent 2016 hepatitis A outbreak in Canada from frozen fruit is only one of several similar outbreaks that have occurred in the past in different industrialized countries. Hepatitis A is spread through the faecal-oral route, and although it is more common in less developed nations where poor sanitation conditions are prevalent, improper hygiene during food handling can cause an outbreak.  Identifying the specific molecular subtype of hepatitis A can help trace which cases are associated with a particular outbreak. It is recommended that anyone handling food take proper precautions in food safety in order to prevent further hepatitis A outbreaks. If worried, one should obtain a pre-exposure vaccination to acquire permanent immunity to the virus.

Sierra Delarosa

 

 

References:

 

  1. http://www.phac-aspc.gc.ca/phn-asp/2016/hepatitisa-eng.php
  2. Chironna M, Lopalco P, Prato R, Germinario C, Barbuti S, Quarto M. J Clin Microbiol. 2004;42(6):2825-8. http://dx.doi.org/10.1128/JCM.42.6.2825-2828.2004
  3. Swinkles, H. M. Et al (2014, May 8). Hepatitis A Outbreak in British Columbia, Canada: The Roles of Established Surveillance, Consumer Loyalty Cards and Collaboration, February to May 2012. Eurosurveillance, 19(18), 20792. http://dx.doi.org/10.2807/1560-7917.ES2014.19.18.20792
  4. Hutin YJ, Pool V, Cramer EH, Nainan OV, Weth J, Williams IT, et al. A multistate outbreak of hepatitis A. National hepatitis A investigation team. N Engl J Med. 1999;340(8):595-602.
    http://dx.doi.org/10.1056/NEJM199902253400802
  5. Gillesberg Lassen S, Soborg B, Midgley SE, Steens A, Vold L, Stene-Johansen K, et al. Ongoing multi-strain food-borne hepatitis A outbreak with frozen berries as suspected vehicle: four Nordic countries affected, October 2012 to April 2013. Euro Surveill. 2013;18(17):pii=20467.
  6. Nordic outbreak investigation team. Joint analysis by the Nordic countries of a hepatitis A outbreak, October 2012 to June 2013: frozen strawberries suspected. Euro Surveill. 2013;18(27):pii=20520.
  7. http://www.cdc.gov/hepatitis/Outbreaks/2013/A1b-03-31/
  8. Heymann DL. Hepatitis, viral. In: Control of communicable diseases manual. 19th ed. Washington, DC: American Public Health Association; 2008. p. 278-84.
  9. Victor, J. C., PhD, MPH. Et al (2007, October 25). Hepatitis A Vaccine versus Immune Globulin for Postexposure Prophylaxis. The New England Journal of Medicine,357, 1685-1694. doi:10.1056/NEJMoa070546
  10. http://www.cbc.ca/news/canada/nova-scotia/costco-hepatitis-a-vaccination-clinics-1.3541908

The Zika Crisis

mosquitoIn 2015, the Zika virus outbreak began in the northeast region of Brazil. According to the World Health Organization, there has been 3174 suspected cases of microcephaly in Brazil since January 2, 2016, including 38 deaths (1). The northeastern region of Brazil continues to be the area most affected, with the highest number of suspected cases. On April 13, 2016, the US Centers for Disease Control and Prevention (CDC) published a paper in The New England Journal of Medicine which concluded that there is a direct causal relationship between prenatal exposure to Zika virus and the outcome of microcephaly and brain abnormalities in the exposed infants (2). While the common symptoms of Zika infection are fever, rash, joint pain, and conjunctivitis lasting from several days to a week after exposure from an infected mosquito’s bite, a recent study recounts two cases of patients who had contracted the Zika virus and later succumbed to acute disseminated encephalitis (ADEM) (3).  This is a condition in which the immune system attacks the body, producing swelling in the brain and spinal cord and damaging the myelin which serves to protectively encase nerve fibers. The same study also describes four patients who had Zika and then developed Guillain-Barré syndrome, a condition where the immune system attacks the body’s peripheral myelin.

Zika virus is quickly spread through the bite of the female Aedes aegypti mosquito, a mosquito that is usually associated with warmer climates. This species of mosquito bites during the day. The Pan American Health Organization (PAHO) sent out a warning of the first confirmed Zika virus infection in Brazil on May 2015, and on February 2016, the World Health Organization (WHO) declared Zika virus a public health emergency of international concern (PHEIC). The PAHO lists the following areas where local transmission of Zika virus is active (4): Aruba, Barbados, Belize, Bonaire, Brazil, Colombia, Costa Rica, Cuba, Curacao, Dominica, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Hondruas, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Peurto Rico, Saint Vincent and the Grenadines, Saint Lucia, Saint Martin, Sint Maarten, Suriname, Trinidad and Tobago, US Virgin Islands, and Venezuela. Locally transmitted cases of Zika have been reported in the Commonwealth of Puerto Rico, the US Virgin Islands, and American Samoa. There is potential for Zika virus to continue to spread to other countries due to the expanding range of the Aedes aegypti mosquito. A population of this species not carrying Zika was found in Capitol Hill, Washington, DC. Genetic analysis revealed that this particular mosquito population survived five winters in the area (5). Although theAedes aegypti is the species most responsible for spreading the Zika virus, other mosquito species in the Aedes genus can also transmit it to humans. Once the virus enters the bloodstream of a human through the bite of a female mosquito (the male mosquitoes do not bite), another female mosquito can acquire Zika by feeding upon the same host, which can then go on to infect another human. In an area with many Aedes mosquitoes, the process will repeat itself exponentially, leading to widespread viral transmission. A possible solution can be to use genetically modified mosquitoes that are male which reproduce with local female mosquitoes to yield offspring which do not live past the pupae stage. Oxitec (6), a British biotechnology company, developed such a mosquito which has already been released and tested successfully in the Cayman Islands in 2010, leading to a drastic 80 percent reduction in population of Aedes aegypti. Release of the same strain of GMO mosquitoes in the suburb of Juazeiro, Brazil in 2011 resulted in a 81-95 percent reduction of Aedes aegypti in the test region. It is also possible to breed mosquitoes to be genetically resistant to diseases such as dengue, malaria, yellow fever and Zika. Gamma radiation is being used in Brazil to sterilize male mosquitoes. Moscamed, a non-profit organization based in Brazil, took to breeding 12 million male mosquitoes per week, sterilizing them with the cobalt-60 irradiator, and then releasing them into select high-risk areas (7). The released sterile males mosquitoes then meet wild female mosquitoes, but no offspring can be produced. As there is no vaccine available right now, the current method of battling Zika virus is to reduce the population of Aedes mosquitoes.

It has been found that the Zika virus can also be transmitted sexually from an infected human male to his sexual partners via vaginal or anal sex (8), and that the virus can remain for a longer duration in semen than in blood. As of now, it is not known whether a woman can sexually spread Zika virus, or if it can be transmitted through saliva or vaginal fluids. Couples who are pregnant, or men who have travelled to areas affected by Zika are advised by the CDC to abstain from sex or use condoms.

The Zika virus is in the Flavivirus genus of viruses, which also include the West Nile virus, dengue virus, tick-borne encephalitis virus, and yellow fever virus. As a flavivirus, the Zika virus is enveloped, has a capsid of icosahedral symmetry, and contains a single-stranded positive-sense RNA genome. The Zika genome is about 10.8 kilobase pairs long. The positive-sense RNA is significant because once the virus enters the host cell, this RNA viral genome can be directly translated into a viral polypeptide, which is then cleaved into structural proteins and proteins to aid in the replication process. The envelope (E) glycoprotein protruding from the membrane of the virus is used for attachment and entrance into human cells.  For the development of a potential vaccine for Zika virus, a segment of the E glycoprotein unique to the Zika virus can be used in the vaccine to mount an antibody-mediated immune response, possibly conferring immunity from future attacks of the virus.

The expanding range of travel of both humans and mosquitoes have allowed for rapidly widespread transmission of the Zika virus. The head and brain abnormalities caused by prenatal exposure from an infected mother are detrimental, and a direct casual link between the virus and microcephaly/brain defects has been determined by the CDC. For instance, the Zika virus genome was found in the brain of an aborted, infected infant (9) that had microcephaly, and Zika virus antigens were found in the brain of one newborn with microcephaly (10). Autopsies found the presence of Zika virus in the brains of infants with severe microcephaly who died. Pregnant women infected with Zika virus have consistently given birth to infants with microcephaly and other brain abnormalities (11). The CDC further found that women who deliver infants with microcephaly were infected with Zika virus during the first and second trimester of gestation, when the brain starts to form and develop (12). There are two hypotheses directed at explaining how the Zika virus causes birth defects such as microcephaly (13). The first hypothesis posits that the placenta transfers the virus directly from mother to the fetus. The second hypothesis refers to the possible reaction of the placenta in response to Zika, which may contribute to or result in birth defects. Pregnant women are advised not to travel to areas where Zika virus is occurring.

Sierra Delarosa

 

   References

 1) Microcephaly-Brazil. (2016, January 8). Retrieved April 15, 2016, from http://www.who.int/csr/don/8-january-2016-brazil-microcephaly/en/

2) Rasmussen, S. A., M.D., Jamieson, D. J., M.D., Honein, M. A., PhD, & Petersen, L. R., M.D. (n.d.). Zika Virus and Birth Defects — Reviewing the Evidence for Causality. The New England Journal of Medicine. doi:10.1056/NEJMsr1604338

3) American Academy of Neurology. (2016, April 11). Zika virus may now be tied to another brain disease. ScienceDaily. Retrieved April 16, 2016 from www.sciencedaily.com/releases/2016/04/160411082335.htm

4) Countries and territories with autochthonous transmission in the Americas reported in 2015-2016. (n.d.). Retrieved April 15, 2016, fromhttp://www.paho.org/hq/index.php?option=com_content&view=article&id=11603:countries-territories-zika-autochthonous-transmission-americas&catid=8424:contents&Itemid=41696&lang=en

5) Gustin, G. (2016, February 26). Zika Virus Mosquitos Have Been Found…on Capitol Hill. Retrieved April 15, 2016, fromhttp://www.washingtonian.com/2016/02/26/zika-virus-mosquitos-capitol-hill-aedes-aegypti/

6) More on the science: How does oxitec make genetically modified mosquitoes? (n.d.). Retrieved April 15, 2016, fromhttp://www.oxitec.com/oxitec-video/more-on-the-science-how-does-oxitec-make-genetically-modified-mosquitoes/

7) Boadle, A. (2016, February 22). Brazil to fight Zika by sterilizing mosquitoes with gamma rays. Reuters. Retrieved April 15, 2016, from http://www.reuters.com/article/us-health-zika-radiation-idUSKCN0VV2JK

8) Zika and Sexual Transmission. (2016, February 21). Retrieved April 15, 2016, from http://www.cdc.gov/zika/transmission/sexual-transmission.html

9) Mlakar, J., M.D. et al (March 10, 2016). Zika Virus Associated with Microcephaly. The New England Journal of Medicine, 374, 951-958. DOI: 10.1056/NEJMoa1600651

10) Martines RB, Bhatnagar J, Keating MK, et al. Notes from the Field: Evidence of Zika Virus Infection in Brain and Placental Tissues from Two Congenitally Infected Newborns and Two Fetal Losses — Brazil, 2015. MMWR Morb Mortal Wkly Rep 2016;65, 159–160. DOI:http://dx.doi.org/10.15585/mmwr.mm6506e1

11) Rasmussen, S. A., M.D., Jamieson, D. J., M.D., Honein, M. A., PhD, & Petersen, L. R., M.D. (n.d.). Zika Virus and Birth Defects — Reviewing the Evidence for Causality. The New England Journal of Medicine. doi:10.1056/NEJMsr1604338

12) Rasmussen, S. A., M.D., Jamieson, D. J., M.D., Honein, M. A., PhD, & Petersen, L. R., M.D. (n.d.). Zika Virus and Birth Defects — Reviewing the Evidence for Causality. The New England Journal of Medicine. doi:10.1056/NEJMsr1604338

13) Adibi, J. J., ScD. Et al (2016). Teratogenic effects of the Zika virus and the role of the placenta. The Lancet. http://dx.doi.org/10.1016/S0140-6736(16)00650-4

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